Growing concern about the global environment has led to advances in the conservation of resources and energy. Considerable progress has been made in the development of energy sources that utilize renewable “green” energy, and systems thereof, as energy resources. Fuel cell systems in which hydrogen serves as the energy source have a particularly wide range of applications, such as in alternative automobile engine technology, distributed power sources, and cogeneration technology. Also, the popularization of cellular telephones and other such personal information devices has advanced the development of large-capacity cells to power these devices. One promising technology in this field is fuel cells that make use of hydrogen, methanol, or other such fuel.
FIG. 9 shows the basic structure of a fuel cell. A fuel cell is made up of a) a fuel electrode for producing electrons and protons by reacting a fuel such as hydrogen, b) a solid electrolyte for transmitting the produced protons, and c) an oxygen electrode for reacting electrons supplied through an external circuit with oxygen and protons.
The reactions in the electrodes are as follows. First, with the fuel electrode, a fluid fuel that is a liquid or gas reacts with a catalyst on the electrode, with this reaction comprising H2→2H+↑+2e−↑, for example. Charge-separated electrons are transferred from the electrode to an external circuit, and protons are transferred to a proton-conductive electrolyte. The electrolyte serves to transmit just protons, and one whose efficiency is decreased only minimally by the diffusion of fuel, etc., is used.
With the oxygen electrode located across from the fuel electrode, electrons and protons produced by the fuel electrode arrive and react with the oxygen in the air or with oxygen gas in the presence of a catalyst, and water is produced in a reaction comprising O2+4H+↑+4e−↑→2H2O.
The result of above reactions is that electrical power can be obtained from the energy of hydrogen, methanol, and other such renewable energy sources, and since the reaction product is water, there are no environmental problems.
Carbon materials are widely used as the above-mentioned electrode materials. For instance, carbon black, activated carbon, graphite, conductive carbon, and other such carbon materials are formed into porous body and used as electrodes.
Methods for forming porous carbon have been studied in an effort to enhance the performance of these electrodes. For instance, one of the methods that have been proposed involves increasing the specific surface area and carbonizing an organic aerogel of a phenol polymer which is a precursor of carbon having numerous microscopic pores and a low density, in order to make the electrode reaction more efficient (such as in WO94/22943).
Another method that has been proposed involves carbonizing an organic gel of a polyimide polymer which is a precursor of carbon having numerous microscopic pores and a low density (such as in Japanese Unexamined Patent Publication 2000-154273).